1. Field of the Invention
The present invention relates to a rubber composition for a tire tread and a pneumatic tire using the rubber composition, and more particularly, to a rubber composition for a tire tread which provides both an excellent controllability (herein after referred to as controllability) and an excellent vibration quality in a car ride (hereinafter referred to as ride quality) throughout its life, and a pneumatic tire using the rubber composition.
2. Description of the Related Art
Due to the recent higher power, the greater functionality, and the longer life among automobiles, it is required to provide tires achieving high levels in controllability and in ride quality simultaneously and maintain the performances on the road throughout its life. Particularly, as tires for passenger cars change from bias tires to radial tires and the aspect ratio of radial tires changes from 82 to 70, and further to 65, ride quality is not always improved even though controllability is remarkably improved. Therefore, it is strongly desired that both properties simultaneously exhibit high levels.
In order to satisfy the above-mentioned requirements, various rubber additives for a tire tread have been discussed. For example, regarding a vulcanization accelerator, Japanese Patent Application Laid-Open (JP-A) No. 58-87138 discloses that the resistant to thermoset and appearance of a tire in the final period of its use can be improved by using a rubber composition comprising a combination of a specific antioxidant and a specific vulcanization accelerator, yet nothing is mentioned about the improvement of tire performance, e.g., controllability and ride quality. In JP-A No. 56-139542, a specific vulcanization accelerator is disclosed, and it is therein described that the workability of a rubber composition, especially the scorching property upon kneading, can be improved by using this vulcanization accelerator, yet nothing is mentioned about tire performance using the vulcanization accelerator.